In open-end spinning machines of one previously proposed type, twisted yarn is formed by continuously depositing discrete fibres on an interior fibre-collecting surface of a spinning rotor, continuously removing them from the surface by twisting them into a tail end of a yarn formed thereby, and drawing off the continuously formed twisted yarn.
Spinning rotors for apparatus of this type have hitherto been formed as a hollow body of revolution about the rotary axis, with an inner surface which comprises two coaxial frusto-conical portions joined together at their regions of maximum diameter to provide an axially localised fibre collecting surface on which the discrete fibres are deposited and compacted before being twisted into the tail end of yarn and drawn off as twisted yarn.
Previously, such spinning rotors have been turned on a lathe from a solid piece of material and, due to the internal and external faces of the rotor being non-cylindrical, there have been difficulties regarding machining. It will be appreciated that by using a solid piece of material for manufacture, operations become costly and time consuming. Furthermore, there is the disadvantage that cutting marks are caused by the lathe tool and may have to be removed by further machining.
When using material in cast form for the spinning rotor there is the disadvantage that defects such as cracks or blow holes are present within the material. These defects may cause imperfections in the surface of the rotor and also when a spinning rotor is rotated at very high speeds, there is some danger of fracture of the rotor. Furthermore, cast rotors are usually relatively heavy and tend to accentuate the problems encountered when rotating a body at high speeds, such for example as those created by out-of-balance loads, excessive bearing wear, high power consumption required to drive the rotor and high braking energy required to stop the rotor.
In addition, the cutting marks caused by the lathe tool in forming the internal surfaces of the spinning rotor are a contributory factor to rotor wear when under the abrasive action of the fibres within the rotor. Similarly, when using material in cast form for the spinning rotor, the surface defects such as cracks or blow holes also contribute toward rotor wear under the abrasive action of the fibres within the rotor.